Error: Failed to collect page data for /api/auth/[...nextauth]

[brielov]

I'm trying to deploy a nextjs app to Fly.io. Fly.io uses docker and even though I've set environment variables, it seems that whenever I run next build, next executes my code (I guess for some sort of caching or static thing) and then it fails because of some database connection. This happens on an API route, specifically /api/auth/[...nextauth].

Collecting page data  ..LibsqlError: URL_INVALID: The URL 'undefined' is not in a valid format
    at parseUri (/node_modules/@libsql/core/lib-cjs/uri.js:12:15)
    at expandConfig (/node_modules/@libsql/core/lib-cjs/config.js:39:39)
    at createClient (/node_modules/@libsql/client/lib-cjs/node.js:28:52)
    at 8104 (/.next/server/app/api/auth/[...nextauth]/route.js:389:26407)
    at t (/.next/server/webpack-runtime.js:1:127)
    at r (/.next/server/app/api/auth/[...nextauth]/route.js:450:19418)
    at /.next/server/app/api/auth/[...nextauth]/route.js:450:19445
    at t.X (/.next/server/webpack-runtime.js:1:1191)
    at /.next/server/app/api/auth/[...nextauth]/route.js:450:19431
    at Object.<anonymous> (/.next/server/app/api/auth/[...nextauth]/route.js:450:19472) {
  code: 'URL_INVALID',
  rawCode: undefined,
  [cause]: undefined
}

I don't understand this. Environment variables should be read at runtime, not build time. And if this is failing, I can only guess that nextjs is running my code in some way, otherwise, it should only transpile and libsql should never be executed.

Anyway, how can I disable this behavior?